Unit is named the Graptolite Canyon Member of the Post River Formation for Graptolite Canyon, McGrath 1:250,000 quad, AK. Consists predominantly of graptolitic shale; also contains banded siliceous mudstone. Conformably overlies the upper siltstone member; conformably underlies the limestone member; both of the Post River Formation. Thickness is about 220 m at type; overall thickness is 300 m. Age is Early Ordovician (Arenig) through middle Early Silurian.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
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